It has previously been proposed--see the referenced U.S. Pat. No. 4,064,482, assigned to the assignee of the present application, the disclosure of which is hereby incorporated by reference, to provide inductive transducers located adjacent the wheels of the vehicle, which pick up signals from the tires of the vehicle representative of individual tire pressure, and to transmit the signals, via a wave-shaping circuit, to a shift register. The system is so arranged that the shift register which receives the signals from a transducer of one vehicle wheel is reset by signals received from a transducer of another vehicle wheel, for example at the side opposite to the first, so that the pulse train derived from the respective transducers of oppositely located wheels are compared. If a limiting value for the tire pressure in one side is reached, no signals are transmitted to the associated shift register which, then, is no longer reset and is loaded, rather, by the signals from the opposite wheel. After a few revolutions, the shift register will be full and provide an overflow signal which is connected to an alarm circuit providing an alarm output indication, for example by energizing a warning lamp, that the respective shift register is full, thus indicating incorrect tire pressure of one of the wheels.
The warning light, or other warning indication, provides an output indicating that something is amiss. It does not, however, provide an output indication which one of the vehicle wheels has air pressure which is too low. Due to the comparison of signals from various wheels, no warning indication will be provided if, for example, two oppositely located wheels lose pressure essentially simultaneously, which, for example, may be the case if the vehicle tires are damaged by running over a sharp cross bar, or the like.